Date Added: Oct 2010
To achieve fast link failure detection in all-optical networks, monitoring-cycles (m-cycles) are introduced at the optical layer to reduce the number of required monitoring devices (or monitors). Each m-cycle is equipped with a monitor and a pair of optical transceivers to transmit an optical supervisory signal. A set of m-cycles can be found to form a cycle cover of the network. If a link fails, optical supervisory signals inside the m-cycles passing through this link will be disrupted, and the corresponding monitors will alarm due to Loss of Light (LoL). This gives an alarm code to localize the failed link.